The invention relates generally to techniques of bonding dissimilar materials together and more particularly to processes for joining plastic to metal and the product formed thereby.
The use of ultrasonic energy for bonding metals together has been known for years. Similarly, insert injection molding techniques for forming containers and other items from a single, homogenous starting plastic material are known.
What is not known and has not been done before is successfully bonding a plastic material, such as polyethylene or an ABS resin, to a metal such as aluminum or steel.
The novel process disclosed and claimed herein has particular application to the manufacture of beverage containers and, more generally, containers for a wide variety of liquids. Currently, containers for beverages such as soft drinks, beer and ale are made from glass only, metal only or plastic only. Each container has its own attendant advantages and disadvantages. For example, glass containers are rather sturdy and can be sterilized for reuse but are fragile, rather easily broken and weigh considerably more than plastic or metal containers. The weight factor causes considerable added costs in shipping and handling. Metal containers made of steel and aluminum are lighter in weight and are more readily chilled than glass containers. However, they cannot be reused without recycling of the containers into basic metal and reforming of the metal into a new container. Nevertheless, the economics are such that, given the popularity of metal containers and the increasing use of recycling of such containers due to energy conservation and short supply of raw material factors, particularly those made from aluminum, into new containers, the marketing of beverages in metal cans is most successful.
More recently, plastic beverage bottles or containers have appeared in the market place and have enjoyed rather widespread popularity. For example, plastic containers have screw-off caps over a small neck opening which makes the container easier to drink from and more sanitary. Conversely, metal containers, particularly those made from aluminum, have tops that are difficult to open and somewhat dangerous to use in that the opened top leaves a sharp, exposed edge that may cut the lip or mouth of the user. Plastic containers can be recycled into new beverage containers with a recovery factor of about 25% of the starting material. Aluminum is recycled more efficiently, however, in that about 65% of the starting material may be recovered.
A singular and significant disadvantage of plastic only containers is that they may explode when stored at elevated temperatures. By elevated temperatures we mean as low as 85.degree. to 90.degree. F.
Accordingly, significant advantages are obtained by the present invention wherein plastic and metal are successfully bonded together and a useful product is obtained thereby. Specifically, we disclose a beverage container made of aluminum and plastic which has the best features of aluminum only and plastic only containers. In a preferred embodiment, the beverage container has an aluminum base with a plastic top joined thereto having a screw-off cap. The container is thus safer to use than a plastic container because it will not explode and safer to use than a metal container because it has the sanitary and safety advantages of either all glass or all plastic containers.
Most significantly, the recycling recovery rate of the aluminum-plastic beverage container of this invention is almost as great as that of an all aluminum container. Specifically, the aluminum base is 65% recoverable while the plastic top is 25% recoverable. Present day recycling centers and plants may be used because the plastic and metal components are very easily dissociated and separately recovered in the recycling process.